Amazon MP3 and Walmart weren't immune to pressure for variable song pricing and today started quietly charging higher prices for popular songs. In particular, about 10 of the top 100 songs on Amazon now meet the same $1.29 prices as similar tracks on iTunes, including recent Beyonce, Britney Spears and The Fray songs. Walmart's store, in turn, is now charging $1.24 per song for some titles and h
